Package-unit incinerators are in wide and increasing use for the disposal of combustible solid waste materials due to the shortage of land-fill disposal sites, governmental regulations controlling contaminated waste and air pollution from open burning, energy recovery possibilities from incineration, and ease of disposal by incineration on-site.
For example, hospitals produce relatively large quantities of combustible waste, much of which may be contaminated material, they are usually located where air pollution is particularly objectionable, and they normally have considerable heat requirements which may be supplied from incineration.
Modern package-unit incinerators that can meet current clean air codes operate on the controlled air principal, and they are of the dual chamber type. Partial combustion takes place pyrolitically in the lower primary chamber in a "starved" air or less than stoichiometric atmosphere. Combustion of the unburned gasses from the primary chamber is completed in the upper secondary chamber in an excess air atmosphere.
More and more incinerators of this type in sizes of 1000 lbs/hr and larger are being used in heat recovery systems. In these systems, the hot gas effluent from the burning waste is ducted to a nearby steam boiler, hot water heater or other type of heat exchanger where the energy is utilized.
There are several problems that hamper the operation of these incineration-heat recovery systems. One problem is that the incinerators are generally batch loaded by ram type feeders. Every time a batch or charge is loaded there is an inrush of cold air that upsets the air balance and causes a momentary temperature drop in the primary chamber. Following each newly loaded batch, there is a surge of easily liberated volatiles into the secondary chamber causing a sharp upper chamber temperature rise which subsides gradually until the next charge causes another peak. This tends to cause smoke from the stack and reduced combustions efficiency during the surge part of the cycle. This not only creates unacceptable air pollution, but also results in coating of the heat exchanger tubes causing heat transfer inefficiency and produces undesirable fluctuations and losses in the desired flow of recovered energy. The dwindling supply of gasses to the secondary chamber during each charging cycle also produces a constantly changing fuel-air ratio in a fixed air flow system.
To be safe, combustion air must be supplied to the secondary chamber of such an incinerator in the proper air-fuel ratio to attempt to produce clean burning during the surges. As an economically practical matter, the fluctuating waste gas flow cannot be matched with a proportional air flow that would maintain a fixed air-fuel ratio during the cycles. Therefore, air is supplied in a quantity that is generally adequate for the peak gas flow but is considerably in excess for the reduced gas flow as burning of the charge progresses, so that the temperature drops rapidly as excess air increases, and the average temperature falls far below the temperature of optimum air-fuel ratio burning.
A batch loading system is expensive to automate completely. Therefore, most systems are monitored by an operator who typically delays or completely misses a loading period from time to time. This causes average combustion temperature and therefore the recovered energy flow to fall even farther short of the desired level.
The problems connected with fluctuating waste gas flow to the secondary chamber can be largely eliminated by feeding the waste into the incinerator continuously at the desired burning rate rather than in batches. A great advantage is obtained by the resultant relatively constant flow of waste gas to which the air flow can be matched in a fixed near-optimum ratio to produce more nearly maximum temperature as well as cleaner burning in the secondary chamber.
The compactor-feeder of the present invention is designed to provide a continuous supply of compacted solid waste to a package-unit incinerator or other combustion chambers and is expected to improve the efficiency of converting waste to heat by a 15-20% factor. Compaction of the waste gives the waste enough structural integrity to be pushed into the firebed of the incinerator, and it forms a dense moving plug of compacted waste which forms an effective air seal for the primary incinerator chamber and also prevents heat from the incinerator from prematurely igniting the incoming waste.
Practical continuous feeding becomes feasible with the unique combination of structural features of the presently proposed compactor-feeder which should enable it to automatically respond to an object or quantity of waste which is insufficiently compactable for passage into the incinerator and to a supply of waste insufficient to form a suitably compacted plug, while also having the capability to prevent fire getting to the feed hopper from the incinerator under those conditions, as well as while normally operating, stopping and starting, and shutting down, all with waste combustion in process and the incinerator at operating temperature.
U.S. Pat. Nos. 1,004,126, 1,224,993, 2,351,410, 2,402,849, 3,230,866, and 3,815,521 disclose convergent conveyors for feeding various materials. U.S. Pat. Nos. 1,450,127, 1,463,300, and 2,095,446 disclose doors used in connection with feeding various fuels. U.S. Pat. No. 3,457,882 discloses a plug of waste material used as an air seal. U.S. Pat. Nos. 987,911, 2,792,131, 2,978,997, and 3,473,493 also relate to furnace feeding. None of the above-listed patents discloses or suggests the combination of elements or the methods which are considered to make the present invention patentable, workable and advantageous for feeding waste incinerators.